Remove file I/O from tests that don't need it (#11182)

# Description

This PR implements modifications to command tests that write unnecessary
json and csv to disk then load it with open, by using nuon literals
instead.

- Fixes #7189



# User-Facing Changes
None

# Tests + Formatting
This only affects existing tests, which still pass.

crates/nu-command/tests/commands/default.rs

@@ -1,13 +1,8 @@
-use nu_test_support::fs::Stub::FileWithContentToBeTrimmed;
-use nu_test_support::playground::Playground;
 use nu_test_support::{nu, pipeline};
 
 #[test]
 fn adds_row_data_if_column_missing() {
-    Playground::setup("default_test_1", |dirs, sandbox| {
-        sandbox.with_files(vec![FileWithContentToBeTrimmed(
-            "los_tres_amigos.json",
-            r#"
+    let sample = r#"
                 {
                     "amigos": [
                         {"name":   "Yehuda"},
@@ -16,22 +11,19 @@ fn adds_row_data_if_column_missing() {
                         {"name":"GorbyPuff"}
                     ]
                 }
-            "#,
-        )]);
+            "#;
 
-        let actual = nu!(
-            cwd: dirs.test(), pipeline(
-            "
-                open los_tres_amigos.json
+    let actual = nu!(pipeline(&format!(
+        "
+                {sample}
                 | get amigos
                 | default 1 rusty_luck
                 | where rusty_luck == 1
                 | length
             "
-        ));
+    )));
 
-        assert_eq!(actual.out, "2");
-    });
+    assert_eq!(actual.out, "2");
 }
 
 #[test]